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> We are agreed on all your comments. Especially agreed that injection well pressure bleeds off over time and in the process displaces petroleum towards the production well in theory. But a pressure dome exist for a long time in the injection area. I know that that same waste water sometimes comes out the production well quicker than wanted and has to be separated.
I was talking about waste- water disposal wells which is a closed system, not an enhanced production operation where pressure does "bleed" off through the production wells. The "pressure dome" can store a tremendous amount of energy in the case of the long-term injection of wastes. We agree that the pressure and injected fluids can cause movement on existing fractures and result in earthquakes but it sounds like you are saying that the resulting quake only releases the energy stored in the rocks before the injection began. I think there is a very real possibility that the quake would also release at least part of the energy stored in the injection zone because of the injection wells.
If a short-term, limited injection operation of the type we see in the fracking process releases enough energy to cause a magnitude 2 quake, how much more energy might come from a long-term injection operation where much greater amounts of energy is stored in the ground?
I will have to say that this is all hypothetical. I haven't heard of large magnitude earthquakes being associated with long-term disposal wells but many of those operations are still in process.
This is just a bit of speculation. The realities will prevail over time and the hype will be overcome. That is the way it has always been.
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> My over all point about energy was that larger quakes occur because the stress in the rocks already exist as opposed to the claim that the injection pressure energy was releasing 3.0-5.7 quakes in and of itself. While it is sometimes owing to triggering a reactivated fault it can also occur in small swarms as the host rock is inflated. I think the pressure does make some injection well fields susceptible to being triggered by distant stronger quakes owing to the collective buoyancy effect the reinflated field has stored up making rock shifting easier to trigger.
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> I used to keep up with the studies from the Imperial Valley Geothermal production along with the liquid sodium reactor near Barstow but am not current. Seems like I remember that there was a very quickly noted slippage on the San Andreas arm where the salt water was being injected. This should have been expected as the fault sides are very well defined with lower friction than most. I think the water easily overcame the remaining friction and put the south west side on skids. My issue was that the hot water being pumped up while mineralized was still fresh water. Rather than pumping water from Lake Senyore(sp) they used high brine from the Salton Sea and ruining a fresh water aquifer for possible human use when Palm Springs runs dry.( grin)
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> I was reading today about a 2.0-3.0 quake in the northern UK which was "caused " by fracking activity as if it were the fracking itself vs triggering an already stressed fault. I am trying to get back to the article to see the details. Geologist aren't immune from jumping to unsupported conclusions and getting published because their pear reviewers are too lazy to read beyond the abstract.
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> Eman
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> >________________________________
> > From: fossrme fossrme@...
> >To: geology2@yahoogroups.com
> >Sent: Monday, July 15, 2013 8:25 PM
> >Subject: [Geology2] Re: Quake Primer wasEarly Warning Signs ..Long
> >
> >
> >
> >
> >
> >--- In geology2@yahoogroups.com, MEM wrote:
> >>
> >> I believe I addressed all this in the original post:Â pressure in the injection wells disspates over days to weeks into the pores of the rock strata it isn't just a static vessel pumped to max pressure.
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> >If by "dissipates" you mean that the pressure zone spreads, that is true, but it doesn't disappear. The pores of the rocks are already filled with native fluids so the injected fluid drives flow away from the well and creates a pressure gradient with the well at the center. Some of the pressure is absorbed by the compressibility of the natural materials and then exists as potential energy but much of it remains as highly pressurized fluids contained in the injection zone. The energy isn't lost. The most important principle of deep well injection is that those pressured fluids are contained in a zone that does not have a connection to the surface that would allow the fluids to come back up. Abandoned and unplugged oil wells have been the cause of many contamination incidents where salt water moved to the surface under the pressure of injection wells some distance away.
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> >>  I also tried to note there is a big difference in drilling/fracking tremors vs. those alleged actions which "trigger" quakes when "previously unknown" faults are reactivated. The energy potential is drastically different in scale. Potential energy comes from the pressurized water and, from stresses in the ground which may be there due to oil/gas extraction deflation or, from stressed ancient faults. The former are relatively small and the latter are small to medium as evidenced by the 5+ which happened in Prague, OK.
> >>
> >> Think a rusty spring-loaded lever that has been sprayed with penetrating oil. Eventually, depending on how much tension in the spring and how well the oil dissolves the rust bonds the lever can swing at any time. With two blocks of rock, under tension and with a fault down the middle, the fluid slowly wedges them apart and lubricates the faces. When the friction is overcome(aka sufficiently relieved) , there will be a rupture along the fault.Â
> >>
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> >I think there is a lot of assumption about what is happening in the subsurface. I haven't heard the terms "drilling tremors", or "fracking tremors" but I assume they are the small quakes up to about a magnitude of 3 or so. We can all agree that lubrication of existing fault planes can result in movement and seismic events. It also makes sense to say that injection increases pore pressure and can provide fluids that might facilitate movement along existing faults. I think that is what you are saying above but I'm not sure.
> >> The study also addressed the potential for a distant large quake to trigger a swarm of tremors in an injection field followed by a larger quake in that field. This may have been the case in Prague, OK
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> >> Eman.
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